Quality control in the development stage of the mo

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Quality control in the development stage of positive PS plate

at present, the positive PS plate commonly used in printing needs to be developed before it can be printed on the machine after it is normally exposed by gallium iodide lamp. There are chemical changes in the development process of the positive PS version. 2. Place the clean samples in order in the sample basket; Then put it into the low-temperature tank. There are physical changes in the cold tank. The chemical change is manifested by the decomposition of the photosensitizer after exposure, and the rearrangement of the molecular structure to form ninhydric acid, which reacts with alkali to form a water-soluble salt; The physical change is that the exposed photosensitive layer is stripped away from the plate base. Therefore, the factors that affect the performance of developer include both chemical factors and physical factors, which constitute a complex process. In order to achieve the ideal development effect, we should scientifically analyze and strictly control the influencing factors of each link in the development process, so as to ensure the development quality

I. in the preparation stage, there are roughly two types of developing materials used together with PS version: solid developing powder and liquid developing concentrate. No matter which developing material is used, the developer must be adjusted to the appropriate concentration before it is used for development. The following points should be paid attention to in this link:

1. The materials should be fully mixed before taking.

solid developing materials are a mixture of developer, inhibitor, wetting agent and other components. For the directly mixed developing powder, due to the different specific gravity, particle shape and size of each component, the components with small particle size and large proportion are centrally distributed at the bottom of the container after bumping during transportation. In this case, take the developing powder at the upper and lower parts of the container respectively to prepare a developing solution, and develop the same PS plate under the same developing conditions, and the developing effect is obviously different; For the developing powder made by powder spraying process, the above problems also exist due to the different particle sizes. Therefore, when directly taking the developing powder to prepare the developing solution, the developing powder should be fully mixed first

when diluting and preparing developer with developer concentrate, attention should also be paid to the problem of mixing. After the concentrated solution is standing, some components with poor solubility will settle to the bottom of the container due to the action of gravity, and the components in the solution are not evenly distributed. The experiment shows that the developing effect is not good when only the upper solution is mixed in proportion. Therefore, when taking the concentrated solution to prepare the developer, the problem of mixing cannot be ignored

2. deionized water is selected as the water for liquid preparation

generally, there are no special requirements for the water used to prepare developer gb/t6096 (2) 009 "safety belt test methods". Users basically use tap water or deep well water. These water, which looks very clear on the surface, essentially contains many invisible impurities, which can be roughly divided into five categories: electrolyte, organic matter, particles, microorganisms, dissolved gas, etc. The existence of these impurities will have a negative impact on the development of PS version. The most obvious point is that it causes the developer to scale. The developer is an alkaline solution with a pH value of about 13. The scaling theory tells us that sodium silicate, which is one of the components of the developer, is a substance easy to scale. Coupled with the comprehensive effect of calcium, magnesium, iron and other impurity ions introduced by water, it is easier to cause the scaling of alkaline developer. The direct impact is to cause the nozzle of the developer to be blocked, so that the developer spray is uneven, thus affecting the development quality. Therefore, it is best to choose deionized water as the water for liquid preparation to slow down the scaling process of the developer

3. confirm the optimal concentration of developer

different models of positive PS version have development materials used with it, and the manufacturer will also provide the corresponding proportion of prepared developer. For example, in the instruction manual of a certain brand of developing powder, it is suggested that "a bottle of developing powder is completely dissolved into a concentrated solution with 5:1 warm water, and then the concentrated solution is diluted at the ratio of 1:6 during development". The dilution ratio of 1:6 mentioned here is a widely applicable dilution ratio obtained by the manufacturer through a large number of experiments. For a user, before giving a new batch of positive PS plates formal development, trial development should also be carried out to determine the best concentration of the developer suitable for this batch of plates. Here is a simple and practical method: develop the PS version with a printing scale for 30 to 60 seconds, and observe it with a high-power magnifying glass. If 98% to 99% of the hollow spots are not pasted and 1% to 2% of the small black spots are not lost, it indicates that the concentration of the developer is appropriate

II. After the preparation work in the development stage is ready, the positive PS version can be formally developed. It is necessary to completely remove the photosensitive layer that has been decomposed by light on the layout, and make the photosensitive layer that has not seen light not dissolved. To achieve this goal, we should start with the factors that affect the development quality - Developer temperature, development time and developer concentration, and control the development conditions within an optimal range, so as to ensure the development quality

1. control the appropriate development temperature

heat is required for ninhydrin hydrolysis, salt formation and salt dissolution in the development process. If the temperature of the developer is too low to provide the heat required for the development process, it will hinder the smooth development; If the temperature of the developer is too high, the unexposed image and text will be dissolved. Theory and practice show that when the temperature exceeds 30C, the binding force between the photosensitive resin and the film-forming resin in the photosensitive layer decreases, and the alkali resistance decreases. Therefore, an appropriate development temperature is one of the prerequisites to ensure good development quality. Generally, it is appropriate to control the developing temperature at 25 ± 2

2. Control the appropriate development time

whether the development time is appropriate directly affects the development quality of PS version. The development time is too long, and the small dots on the layout are easy to be lost; The development time is too short, and the photosensitive layer of the non image part cannot be completely dissolved, which will cause the layout to get dirty. In order to avoid the above phenomenon, the steel ball should be rotated with minimal friction resistance to control the development time between 30 and 120 seconds. For qualified PS version, its development tolerance should reach 120 seconds

3. Maintain the appropriate developer concentration

after several times of development, the effective components in the developer are continuously consumed. Coupled with the role of the photosensitive layer constantly dissolved in the developer, the developing ability of the developer is getting weaker and weaker, so that it cannot meet the development requirements, and the developer shows aging phenomenon. At this time, the developer should be treated as necessary according to the actual situation. When the aging phenomenon is not serious, it is generally taken to supplement an appropriate amount of concentrated solution to maintain the developing ability of the developer. This method is simple and easy, but it should be supplemented at any time. When the developer is seriously aged after being used for a certain period of time, it should be replaced in time

in a word, the quality control of developer is a problem that cannot be ignored to provide automatic power failure protection. Although development is only a link in the PS plate making process, if we can control the quality of this link, it will play a very important role in improving the quality of the whole positive PS plate making process

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